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2016 · Reports on Progress in Physics

A review of metasurfaces: physics and applications

Hou‐Tong Chen, Antoinette J. Taylor, Nanfang Yu

Metamaterials are composed of periodic subwavelength metal/dielectric structures that resonantly couple to the electric and/or magnetic components of the incident electromagnetic fields, exhibiting properties that are not found in nature. This class of micro- and nano-structured artificial media have attracted great interest during the past 15 years and yielded ground-breaking electromagnetic and photonic phenomena. However, the high losses and strong dispersion associated with the resonant responses and the use of metallic structures, as well as the difficulty in fabricating the micro- and nanoscale 3D structures, have hindered practical applications of metamaterials. Planar metamaterials with subwavelength thickness, or metasurfaces, consisting of single-layer or few-layer stacks of planar structures, can be readily fabricated using lithography and nanoprinting methods, and the ultrathin thickness in the wave propagation direction can greatly suppress the undesirable losses. Metasurfaces enable a spatially varying optical response (e.g. scattering amplitude, phase, and polarization), mold optical wavefronts into shapes that can be designed at will, and facilitate the integration of functional materials to accomplish active control and greatly enhanced nonlinear response. This paper reviews recent progress in the physics of metasurfaces operating at wavelengths ranging from microwave to visible. We provide an overview of key metasurface concepts such as anomalous reflection and refraction, and introduce metasurfaces based on the Pancharatnam-Berry phase and Huygens' metasurfaces, as well as their use in wavefront shaping and beam forming applications, followed by a discussion of polarization conversion in few-layer metasurfaces and their related properties. An overview of dielectric metasurfaces reveals their ability to realize unique functionalities coupled with Mie resonances and their low ohmic losses. We also describe metasurfaces for wave guidance and radiation control, as well as active and nonlinear metasurfaces. Finally, we conclude by providing our opinions of opportunities and challenges in this rapidly developing research field.

2,524 citations1 viewsFull text
DOI: 10.1088/0034-4885/79/7/076401
2012 · Reports on Progress in Physics

The physics of wind-blown sand and dust

Jasper F. Kok, Eric J. R. Parteli, Timothy I. Michaels, Diana Bou Karam

The transport of sand and dust by wind is a potent erosional force, creates sand dunes and ripples, and loads the atmosphere with suspended dust aerosols. This paper presents an extensive review of the physics of wind-blown sand and dust on Earth and Mars. Specifically, we review the physics of aeolian saltation, the formation and development of sand dunes and ripples, the physics of dust aerosol emission, the weather phenomena that trigger dust storms, and the lifting of dust by dust devils and other small-scale vortices. We also discuss the physics of wind-blown sand and dune formation on Venus and Titan.

1,553 citations0 viewsFull text
DOI: 10.1088/0034-4885/75/10/106901
1970 · Reports on Progress in Physics

The nature of bonds in paper and the behaviour of paper under mechanical strain

C. T. J. Dodson

Work done during the past twenty years on the physics of fibre bonds in paper and the behaviour of paper under mechanical strain is reviewed. The first major section of the article illustrates the chemical nature of the cohesion in paper and reports the results of direct observations on fibre-to-fibre bonds. A statistical theory of the geometry of fibrous networks is shown to be a basis for the characterization of fibre bonding in paper. The second major section is concerned with the mechanical behaviour of paper. This is shown to be a complex subject because paper exhibits almost every known rheological property. Direct, conventional rheological methods, molecular theories and the concept of elastic networks are discussed in this context. Further complications arise from any changes in the water content of the environment. Such effects are conveniently thought of as a competitive process wherein cellulose and water compete for hydrogen bonds for their hydroxyl groups. Not least among the rheological phenomena that paper exhibits is mechanical fracture. This is a discontinuous process that is found to be intimately connected with the mechanical work done on the specimen and is principally governed by its geometrical distortion.

18 citations0 views
DOI: 10.1088/0034-4885/33/1/301